diff --git a/src/main.c b/src/main.c
index 94043b8..cc44877 100644
--- a/src/main.c
+++ b/src/main.c
@@ -550,6 +550,11 @@ sync_chans( main_vars_t *mvars, int ent )
 		  gotchan:
 			mvars->chan = chan;
 			if (boxp) {
+				if (!chan->patterns) {
+					error( "Cannot override mailbox in channel '%s' - no Patterns.\n", channame );
+					mvars->ret = 1;
+					goto gotnone;
+				}
 				mvars->boxlist = 1;
 				for (;;) {
 					nboxp = strpbrk( boxp, ",\n" );
diff --git a/src/mbsync.1 b/src/mbsync.1
index 867b90b..e06d6fe 100644
--- a/src/mbsync.1
+++ b/src/mbsync.1
@@ -367,10 +367,8 @@ Define the Channel \fIname\fR, opening a section for its parameters.
 .TP
 {\fBMaster\fR|\fBSlave\fR} \fB:\fIstore\fB:\fR[\fImailbox\fR]
 Specify the Master resp. Slave Store to be connected by this Channel.
-If \fImailbox\fR is omitted, \fBINBOX\fR is assumed.
-The \fImailbox\fR specification can be overridden by \fBPatterns\fR, which
-in turn can be overridden by a mailbox list in a Channel reference (a Group
-specification or the command line).
+If \fBPatterns\fR are specified, \fImailbox\fR is ignored.
+Otherwise, if \fImailbox\fR is omitted, \fBINBOX\fR is assumed.
 ..
 .TP
 \fBPattern\fR[\fBs\fR] [\fB!\fR]\fIpattern\fR ...
@@ -385,6 +383,9 @@ times); later matches take precedence.
 Note that \fBINBOX\fR is not matched by wildcards, unless it lives under
 \fBPath\fR.
 .br
+The mailbox list selected by \fBPatterns\fR can be overridden by a mailbox
+list in a channel reference (a \fBGroup\fR specification or the command line).
+.br
 Example: "\fBPatterns\fR\ \fI%\ !Trash\fR"
 ..
 .TP
@@ -524,8 +525,9 @@ with the same name on the command line.
 One or more Channels can be specified on the same line.
 .br
 If you supply one or more \fIbox\fRes to a \fIchannel\fR, they will be used
-instead of what is specified in the Channel. The same can be done on the command
-line, except that there newlines can be used as mailbox name separators as well.
+instead of what is specified in the Channel's Patterns.
+The same can be done on the command line, except that there newlines can be
+used as mailbox name separators as well.
 ..
 .TP
 \fBChannel\fR[\fBs\fR] \fIchannel\fR[\fB:\fIbox\fR[\fB,\fR...]] ...